Direct thermal imaging is a technique in which a substrate bearing at least one image-forming layer, which is typically initially colorless, is heated by contact with a thermal printing head to form an image. In direct thermal imaging there is no need for ink, toner, or thermal transfer ribbon. Rather, the chemistry required to form an image is present in the imaging member itself. Direct thermal imaging is commonly used to make black and white images, and is often employed for the printing of, for example, labels and store receipts. There have been described in the prior art numerous attempts to achieve multicolor direct thermal printing. A discussion of various direct thermal color imaging methods is provided in U.S. Pat. No. 6,801,233 B2.
It is known in the art to preheat a thermally activated printing head in a thermal imaging application. For example, U.S. Pat. No. 5,191,357 describes a recording apparatus for performing recording on a recording medium where the apparatus includes a plurality of recording elements and a control unit for selectively providing energy having a level lower than an actual recording level. It is also known to preheat a thermal transfer ink layer in a thermal transfer imaging method. For example, U.S. Pat. No. 5,529,408 discloses a thermal transfer recording method wherein the thermal transfer ink layer is preheated prior to having energy applied thereto in order to initiate transfer of the ink to a receiving material.
As the state of the thermal imaging art advances, efforts continue to be made to provide thermal imaging materials and thermal imaging methods that can meet new performance requirements.